Three color kinescope for sequential color systems



United States Patent Ofiice Patented Sept. 27, 1955 THREE COLORKINESCOPE FOR SEQUENTIAL COLOR SYSTEMS John W. Coltman, Pittsburgh, Pa.,assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application April 18, 1952, Serial No.283,069

8 Claims. (Cl. 313-65) My invention relates to cathode-ray tubes and,more particularly, to cathode-ray tubes used in color television.

In accordance with the prior art of which I am aware, color televisiontubes have been built employing phosphor screens in which the coloredphosphors are applied in strips across the screen. In such an apparatus,it is very difficult to insure that the electron scanning beam willimpinge only on phosphors of the proper color at any given time. If thescanning beam should move slightly off its prescribed course, it wouldproduce information on the screen of the wrong color which wouldobviously produce an undesirable efiect. One method of overcoming thiseffect which has been suggested in the prior art is the employment of aplurality of electrodes extending across the tube parallel to thephosphor strips and located in a plane a substantial distance from theplane of the phosphor strips. By applying proper potentials to theseelectrodes, the direction of the electron beam scanning the phosphorstrips could be so controlled that only phosphor strips of the desiredcomposition would be activated at any given time. However, there aremany disadvantages to this system. The support of such electrodes wouldbe extremely difficult due to their small cross-sectional dimensions andthe great distance over which they extend. The large capacity of suchelectrodes, together with the high potentials necessary to give theelectron scanning beam which is composed of high velocity electronssufficient vertical acceleration to have any substantial eflect,requires relatively high switching currents if rapid switching isdesired.

It is accordingly an object of my invention to provide a colortelevision tube wherein a high degree of control is maintained over thecolors produced.

Another object of my invention is to provide a color television tubeemploying a screen of strip phosphors whereby electrons are allowed toimpinge only on phosphors of a given color at any particular time.

Still another object of my invention is to provide a color televisiontube employing electrons which are carefully controlled for activatingthe color phosphors.

Still another object of my invention is to provide a color televisiontube having two screens, a first of said screens emitting low velocityelectrons in response to electrons of an electron scanning beamimpinging thereon.

An ancillary object of my invention is to provide an improved colortelevision tube.

Still another ancillary object of my invention is to provide a new andnovel electronic apparatus.

The invention with respect to both the organization and the operationthereof, together with other objects and advantages may be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawing, in which:

Figure 1 is a schematic showing of a television tube built in accordancewith my invention;

Fig. 2 is a cross-sectional showing of a small portion of the twoscreens of the tube shown in Fig. 1 when no potentials are being appliedbetween successive conducting strips;

Fig. 3 is a cross-sectional showing of the apparatus shown in Fig. 2when potentials are being applied between successive conducting strips;

Fig. 4 is a large scale cross-sectional showing of a portion of thefirst of the two screens of the tube shown in Fig. 1;

Fig. 5 is a schematic showing of the electrical connections to theconducting strips of the first screen;

Fig. 6 is a graph showing the potentials applied to the conductingstrips of the first screen; and

Fig. 7 is a large scale cross-sectional view showing of a portion of thesecond of the two screens of the tube shown in Fig. 1.

In accordance with my invention, I provide an envelope 8 comprisingglass or other dielectric material. Near one end of the envelope 8, Iprovide an electron gun 10 for producing a beam of relatively highvelocity electrons in accordance with the principles well known in theart.

Near the opposite end of the envelope 8 from the electron gun 10, Iprovide a viewing or picture screen 12 lying generally perpendicular toa line between the screen 12 and the gun 10. The picture screen 12comprises a supporting element 14 of transparent material having coatedthereon, on the side thereof toward the electron gun, a plurality ofstrips 16, 18 and 20 of phosphor material. These strips are so organizedthat successive strips emit different colors of light when electronsimpinge thereon. For example, the phosphor strips may be organized inaccordance with my invention in the following order: Blue, green, red,green, blue, green, red. In this organization there is a green strip 18between each of the blue and red phosphor strips 16, 20. There are,therefore, more green strips 18 than either blue strips 16 or red strips20 and it is desirable that the green strips 18 be slightly narrowerthan either the red strips 20 or the blue strips 16. Though the picturescreen 12 is shown as a separate structure, it may be desirable to usethe end of the envelope 8 as an underlying support for the phosphors.

On top of the layer of phosphor strips is a thin aluminum layer 33,penetrable by electrons, which serves the dual purpose of preventinglight from screen 12 from reaching screen 22, and providing a conductingelectrode by which the potential of screen 12 may be maintained at thedesired value.

A short distance from the picture screen 12 and parallel thereto, thereis a primary or photoelectric screen 22. The photoelectric screen 22lies between the picture screen 12 and the electron gun it). Thephotoelectric screen 22 comprises a supporting element 23 of transparentmaterial. On the side of the supporting element 23 of the photoelectricscreen 22 toward the electron gun 10, there is a layer 24 of electronresponsive phosphor material capable of emitting light when electronsfrom the electron beam of the electron gun It) impinge thereon. Inaccordance with one embodiment of my invention there is coated on thephosphor layer 24 an electron transparent semiconducting metallic lightreflecting layer 25 preferably of aluminum.

On the side of the photoelectric screen 22 toward the picture screen 12,there is a layer 34 of transparent semiconducting material such asproperly deposited tin oxide and coated on top of this layer there are aplurality of strips of electrically conducting material 26. These stripsof electrically conducting material are parallel to the phosphor strips16, 18 and 20 and lie substantially opposite to the blue and redphosphor strips 16, 20. The electrically conducting strips 26 areseparated by a gap 28 of a width substantially equal to the width of thegreen phosphor strips 18. Coated over the electrically conducting strips26 and the region 28 where the semi-conductor is exposed between them isa thin layer 30 of photoelectric material such as cesium antimony. Meansare provided including an electric circuit 32 for impressing variablepotentials between successive strips of electrically conducting material26. The potentials between the successive strips of electricallyconducting material 26 are relatively small since electrons emitted bythe photoelectric layer 30 in the region of the electrically conductingstrips 26 will have relatively low initial velocities and may, therefore, be deflected with relative small energies. Between the layer 34 onscreen 22 and the aluminum coating on screen 12, connections are madefor applying a constant direct-current potential of relative largemagnitude. An electric field is thus established for accelerating theelectrons emitted by the photoelectric screen 22 toward the picturescreen 12.

In the operation of my invention, electrons are emitted in a beam fromthe gun with relatively high velocity. The electron beam is caused toscan the primary screen 22, in the usual manner of a television picture,causing the emission of light from the phosphor material 24 coated onthe primary screen 22. Light traveling from the first phosphor layer 24toward the photoelectric layer and impinging on the conducting strips 26is absorbed or reflected by those strips and will not activate thephotoelectric layer 30. However, the light which passes through betweensuccessive conducting strips 26 will activate the photoelectric layer 30between the successive strips so as to cause the emission of electrons.

When no potentials are applied between successive phosphor strips,electrons, emitted by the photoelectric layer in the regions betweensuccessive conducting strips, travel across the region between thephotoelectric screen 22 and the picture screen 12 in a linesubstantially normal to the plane of the picture screen 12. Theseelectrons, therefore, impinge only on the green phosphor strips 18 as isshown in Fig. 2.

When a potential is placed between successive conducting strips so thatalternate strips are positive with respect to the intermediate strips,the electrons coming from alternate gaps will be given a deflection inone direction and the electrons coming from the remaining gaps will begiven a deflection in the opposite direction. For example, as shown inFig. 3, part of the electrons will be deflected upward and part of theelectrons will be deflected downward so that all of the electrons willimpinge on red phosphor strips. Thus, under this condition, only redlight can be emitted by the picture screen.

If the signals applied to the conducting strips 26 are reversed, thebeams will be moved in the opposite direction and all of the secondaryelectrons will impinge on the blue phosphor strips 16 thereby causingthe emission of blue light from the picture screen 12.

By making the transparent material 23 which separates the conductingstrips 26 and the first phosphor layer 24 very thin, it is possible tomaintain a high degree of resolution during the transformation from thehigh speed electrons emitted by the electron gun 10 to the low speedelectrons emitted by the photoelectric layer 30. Moreover, by the properchoice of materials, it may even be possible to obtain a net gain in thenumber of electrons available, thus producing a brighter final picture.

When the electrons are emitted from the photoelectric layer 30, theyhave very small velocities and, therefore, only a very small potentialbetween successive conducting strips is necessary to produce the desireddeflection in the electron beams extending from the photoelectric layer30 to the picture screen 12.

By employing the construction shown herein, there is no problem ofsupporting the conducting strips and maintaining their separation at auniform distance, as was the case in devices of the prior art. Theapparatus disclosed herein is, therefore, believed to be relativelysimple in construction and it is believed to be a highly dependableapparatus. In addition, the form of the conducting strips is such as toreduce substantially the capacity between the two sets of electrodes.

Although I have shown and described specific embodiments of myinvention, I am aware that other modifications thereof are possible. Myinvention, therefore, is not to be restricted except insofar as isnecessitated by the prior art and the spirit of the invention.

I claim as my invention:

1. A color television tube having therein a viewing screen and aphotoelectric screen, said viewing screen being located near the end ofsaid tube and having thereon a plurality of strips of phosphor emittinga plurality of different colors of light, said phosphor strips lyingparallel to each other, said photoelectric screen being parallel to saidphosphor screen and comprising a layer of supporting material which istransparent to light, a layer of electron responsive phosphor on oneside of said supporting material remote to said viewing screen, a layerof electron-emissive material on the other side of said supportingmaterial facing said viewing screen, a plurality of strips ofelectrically conducting material extending across said electron-emissivematerial in a direction parallel to said phosphor strips.

2. A color television tube having therein a viewing screen and aphotoelectric screen, said viewing screen being located near the end ofsaid tube and having thereon a plurality of strips of phosphor emittinga plurality of different colors of light, said phosphor strips lyingparallel to each other, said photoelectric screen being parallel to saidphosphor screen and comprising a layer of supporting material which istransparent to light, a layer of electron responsive phosphor on oneside of said supporting material remote to said viewing screen, a layerof electron-emissive material on the other side of said supportingmaterial facing said viewing screen, a plurality of strips ofelectrically conducting material extending across said electron-emissivematerial in a direction parallel to said phosphor strips, electrodes foraccelerating the electrons emitted by said electron-emissive materialtoward said viewing screen, each of said conducting strips having awidth substantially equal to the phosphor strip opposite it.

3. A cathode-ray tube comprising an envelope having therein a primaryscreen and a picture screen, said primary screen lying in a planeparallel to the plane of said picture screen, said primary screen havingthereon on the side near said picture screen a plurality of strips ofelectrically conducting material separated from each other, said picturescreen having a plurality of strips of phosphor material, said phosphorstrips lying alternately opposite said conducting strips and oppositethe gaps between said conducting strips, each of said phosphor stripsbeing of substantially the same width as the conducting strips or thegap which is opposite it, means for producing electrons in the region ofthe gaps between successive conducting strips, and electrodes foraccelerating said electrons from the region of said conducting stripstoward said phosphor strips.

4. In combination, a primary screen and a secondary screen, said primaryscreen lying parallel to said secondary screen, a plurality ofconducting strips on said primary screen on the side of that screennearest said secondary screen, said conducting strips being separatedfrom each other by a substantial distance, a plurality of phosphorstrips on said secondary screen on the side nearest said primary screen,said phosphor strips lying parallel to said conducting strips, saidphosphor strips comprising a first phosphor representative of a firstselected color, a second phosphor representative of a second selectedcolor, and a third phosphor material representative of a third selectedcolor, said phosphor strips being arranged in the following order: firstphosphor, second phosphor, third phosphor, second phosphor, firstphosphor, second phosphor, third phosphor; the said second phosphorstrips lying opposite the region between successive conducting strips,means for emitting electrons from the region between the conductingstrips so that the electrons pass through the region between successiveconducting strips, electrodes for accelerating said electrons towardsaid secondary screen.

5. In combination, a primary screen and a secondary screen, said primaryscreen lying parallel to said secondary screen, a plurality ofconducting strips on said primary screen on the side of that screennearest said secondary screen, said conducting strips being separatedfrom each other by a substantial distance, a plurality of phosphorstrips on said secondary screen on the side nearest said primary screen,said phosphor strips lying parallel to said conducting strips, saidphosphor strips comprising a first phosphor representative of a firstselected color, a second phosphor representative of a second selectedcolor, and a third phosphor material representative of a third selectedcolor, means for emitting electrons from the region between theconducting strips so that the electrons pass through the region betweensuccessive conducting strips, electrodes for accelerating said electronstoward said secondary screen.

6. In combination an envelope having therein a primary screen and apicture screen substantially parallel to each other and separated by ashort distance, said picture screen having thereon over difierent areasof said screen a plurality of phosphors capable of producing light of aplurality of colors, said primary screen comprising a layer ofphotoelectric material facing said picture screen, electrodes forproducing an electric field in a first direction parallel to saidprimary screen in the region of a first small portion of said layer,electrodes for producing an electric field in a second directionparallel to said primary screen in the region of a second small portionof said layer, and electrodes for producing an electric field across theregion between said primary screen and said picture screen.

7. A television tube comprising an envelope having therein a primaryscreen and a picture screen substantially parallel to each other, saidprimary screen comprising a rigid sheet of light transparent material, aplurality of strips of electrically conducting material deposited onsaid sheet on the side of said sheet toward said picture screen, and aphotoelectric material in the regions between successive strips, andelectrodes for producing an electric field between said primary screenand said picture screen so as to accelerate electrons emitted by saidphotoelectric layer toward said picture screen.

8. A television tube comprising a primary screen and a picture screenseparated by a short distance from each other and substantially parallelto each other, said primary screen comprising a solid rigid sheet oftransparent material, a plurality of deflecting electrodes deposited onsaid rigid sheet facing said picture screen, and means for emittingelectrons in the region of said electrodes.

References Cited in the file of this patent UNITED STATES PATENTS2,307,188 Bedford Jan. 5, 1943 2,446,791 Schroeder Aug. 10, 19482,568,448 Hansen Sept. 18, 1951 2,573,777 Sziklai Nov. 6, 1951 2,577,038Rose Dec. 4, 1951

